In the following known methods for determining the position of a mobile terminal are described.
Known in the art is a method for determining an identifier of the cell in which a mobile terminal is currently located. This method, called Cell Id, relies on the hypothesis that the geographical coverage of a cell corresponds to that predicted by radio studies. It is possible to refine positioning using round trip delay measurements taken by the base station, which measures the time between the transmission of a frame and the reception of the corresponding answer. Using this measurement, the base station can determine the distance to the mobile with an accuracy of about 80 m. The accuracy of this positioning method is low but is compatible with the usual hardware and software of a mobile terminal. Indeed, the network measurements used by the positioning method are anyway performed when trying to establish a communication to the mobile network.
Furthermore sophisticated positioning methods use the perceived synchronization of frames sent by two adjacent base stations. Knowing the real time difference between the base stations, it is possible to retrieve the position of the terminal relatively to the base stations by performing triangulation. Such a method is known under the name OTD (Observed Time Difference). This method is efficient but requires software changes at the terminal and in the network infrastructure.
Another solution consists in integrating a GPS (Global Positioning System) receiver in the mobile terminal and relying completely on the GPS functionality to determine the position of the terminal. This solution is very accurate but requires expensive hardware modifications in the terminal. Moreover, this solution shows poor efficiency in indoor environment.
A particular object of the present invention is to provide a method for determining the position of a mobile terminal which provides a good accuracy.
Other objects of the invention are to provide a mobile terminal, a localization point and a server connected to a cellular communication network all adapted to perform several steps of this method.